Traditional foundry sand molding processes typically employ a two-part mold consisting of a lower half (drag) and an upper half (cope). These two halves are normally produced using the same process: a sand/binder mixture is poured onto a pattern which forms the molding or rigging cavities. When the sand binders have set, the mold and pattern are turned over and the pattern is extracted from the mold. During the mold closing process, the cope half is turned over again and placed on top the drag, forming a complete mold.
A more advanced molding technique, known as patternless molding, differs from the above in that two solid blocks of sand are molded without the use of a pattern. The mold and rigging cavities are then machined into the sand blocks forming the cope and drag. Again, the cope half is turned over and placed on top the drag during mold closing.
There are several inefficiencies inherent in both processes. First, the cope and drag sections must be thick enough to have sufficient strength to withstand the stresses produced during the turnover processes. The amount of sand and binder used for each mold is thus usually far greater than the amount needed otherwise for strength during the pouring process or that needed for thermal insulation. Second, the turnover and mold closing processes take time. And third, inaccuracies in the molding process (including dimensional changes during the binder curing) can create gaps between the cope and drag. During pouring, metal fills these gaps creating “flash” that must be removed by grinding the resulting casting.
Accordingly, a need exists to improve the efficiency of the casting process by reducing the amount of materials necessary to form the cope and reducing the time required to complete the full mold and reducing the amount of flash.